High-frequency apparatus



fDeC- 10, 1946- T. J. BoRNl-:R ETAL 'HIGH FREQUENCY. APPARATUS FiledJune 17, 45

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Dec.1o,1946. T. J. BOERNER Em 2,412,314

HIGH FREQUENCY' APPARATUS /l Trop/v5 y "Dea 10, 1946. T. .LBOERNR ETAL2,412,314

HIGH FREQUENCY APPARATUS `Filed AJune 1'17, 1943 8 Sheets-Sheet 4 //vVEA/709,5' Tho 0.190 ernen Jcn, ,Sanbo'zv ATTORNEY Dec. 1o, 1946. T JBOERNE'R FAL 2,412314 4 HIGH FREQUENCY APPARATUS 8 Sheets-Sheet 5 FilledJune 17., 1945 Dec. l0, 1946. T, J. BOERNER ET AL 2,412,314

HIGH FREQUENCY 4PPARATUS Filed June 17, 1945 8 Sheets-Sheet 6 l /M/-/vroweb l Dec. l0, 1946. T. J. BOERNER E-rAL 2,412,314

HIGH FREQUENCY APPARATUS Filed June 17, 1945 8 she'ets-sheet 7 IN1/ENTopp o armer anb Dec. 10, 1946. T. J. BOERNER ETAL HIGH FREQUENCYAPPARATUS -8 Sheets-Sheet 8 Filed June 17, 1943 Patented Dec. 10, 1946Y' HIGH-FREQUENCY APPARATUS Thomas James Boerner, Collingswood, and JohnW. Sanborn, Merchantville, N. J., assignors to' Radio Corporation ofAmerica, a corporation of Delaware Application June 17, 1943,seria1N0.491,164

11 Claims.

This invention relates to high frequency'ap- `paratus and especially tothe power amplifier stages of high frequency transmitters.

Oneobject of the invention is to provide improved high frequency vacuumtube power amplifying apparatus and circuits which shall operate at highefficiency and'- in which spurious effects such as parasiticoscillations are minimized,v A further object of our invention is toprovide high frequency amplifying apparatus wherein the frequency ofoperation may readily and conveniently be changed. Y

A further object of the present invention is to provide an improved highfrequency tank circuit for vacuum tubes. A feature of the tank circuitresides in an arrangement of fixed and relatively movable conductorsAwhich are so connected and arranged as to form a variable inductor forthe tank circuit. In this` regard provision is `made for varying thespacing between the conductors of the inductorsystem, thereby .varyingthe effective inductance connected into circuit. y

A further object of the present invention is to .provide an improvedhigh frequency output cirarrangement may readily be adjusted foroperation over avwide range of frequencies,

In brief, certain features of the present invention may be outlined asfollowsz* A push-pull connected vacuum tube driver stage is coupledthrough a condenser-divider arrangement to a push-pull connected vacuumtube power amplifier. The condenser-divider operatesin such a way thatover a wide range of operating frequencies substantially constant radiofrequency excitation is applied to the grids of the y power amplier withconstant direct current voltagev impressed upon the plates of the drivertubes.` Y

2 n secure iiow of equal grid currents over a operating range.

The tank circuit of the power amplifier generally consists of a pair ofconductors fixed in position, having substantially uniformly distributedinductance and capacity and another -pair of similar conductorsinsulatingly supported upon a movable metallic plate. These xed andmovable conductorsV having uniformly distributed electrical capacity andinductance are connected together by exible straps. Mechanicalinstrumentalities `are provided for moving the metallic plate upon whichthe movable conductors are mounted so that the effective separation ofthe conductors may be varied, thereby varying the effective inductanceofthe tank circuit. As the conductors of the tank are moved closertogether, the inductance is increased and, similarly, as the separationbetween the conductors is vincreased the inductance of the tankcircuitis decreased.

A final output circuit is provided coupled to the tank circuit. Thisfinal output circuitalso makes use of conductors havingsubstantiallyuniformly distributed inductance and capacity forming theeffective inductance of the output circuit. Variable and fixedcondensers are also provided which form part of the output circuit. Theunits of the output circuit are mounted as `a single unitary assemblywhich may be variably couwide Apled to the tank circuit withoutsubstantially changing the tuning ofthe output circuit and, furthermore,instrumentalities are provided for changing the tuning of the outputcircuit without substantially altering the coupling thereof with thetank circuit of the power amplifier. I

vReversible electric motors are provided for adjusting neutralizing andtuning condensers ofthe power amplifier stage and output circuit.Further instrumentalities under control offother reversible electricmotors are provided for adjusting the separation of the conductors ofthetank circuit and, hence, the effective electrical inductance thereof andalso for adjusting the coupling between the output circuit assemblyandthe tunable tank circuit. Limit switches' are provided for the motors soas to prevent` them Vfrom over-running in either direction.Instrumentalities are also provided'whereby each Areversible electricmotor drives the variable arm of a potentiometer. Each potentiometersupplies voltage to a separate tuning indicator which may be in the formof a volt meter. In vthis way the tuning indicators give a measure, bytheA respective volt meter readings, of vthe capacityin circuit and'inother cases the amount of couwhich the tank circuit is coupljconstituting the power amplifier 'frequency mum 'ftiibe'se'IjY'lfandIVe-appears in the'tuned'output pling or the amount of inductance in thepower I amplifier tank circuit.

In the drawings:

Figure 1 is a wiring diagram of a push-pull' connected driver-amplifierstage feeding through a condenser-,divider arrangement the gridsrof apair of push-pullz'connected vac'uumtube amplii- A ers of a highfrequency power amplifier'. As il'` lustrated in Figure 1, reversibleelectric motora are provided for varying neutralizing and tuningcondensers, the inductance of the tankfcircuit,

and the coupling between the tank dcircuituof the power amplifier andthe final 'o "i I 1;; Figure 2 is a side elevational "view of apparatusal view ofthe apin'to thesecondary ILISQ'eXcitingthe control gridstubesIVfI and IVSinjphas'e opposition. The carrier 'may be generatedrbyany suitable vac'- uum tube generatorfollowed by amplifiers vand pliersy ,'I-fhesecond'aryj ILI3 is tuned bythe split 'statorgjcoiidenser ICkiII.. The

"circuit comprising'coil IL IB and condense'rs I CI Il I into-the`circuit'las' needed, depending regnen@ employed-f if der to prevent`spurious osc'zillations,` the ds of the" Idriver Y tubes j'IViar'id Y IVE!u are o; ground byloor'rdensers I-CliG' and ECH 'l V passe ssingcor'dnsersfICBll VVand* 1G85 are` also chd into the circu" butareswitched zout rcuitin the range ofhigherf'requenci'es. That icondensers I-Cj'land ICdjwill -serve i'S toigiye sufficient ley-passingtofground jat the p higher frequencies sincefthese condensersjmay l'Over the' 'entire range of frequencies, Y however, ineutif'a-lizingfcnd'ensers` V I-CtiS and ICES', which may-consist ofsectionsl of copper strapadjacent 'the-Aanodes; Yare also employed.'|Ihat is, these neutralizing'fcondensers are ernploye'din'V additinltothesereen grids and'their by-passing circi-iitsVv toi' ground.- over!thev entire operatingrange 'ofJf-reque'ncies. The-use of suchvncutralizing cir-- cuits i'nadditionlto'the screening circuits insuresfreedom 'zfrcr'nf 'spurious voscillations.4 and similar -eiect's.-r r Y'j :Coupling frrii'tiie driver stage, including tubes IN/"Ia'ndIlVIB, 'tothe? final'power amplifier stage cornprisin'gfwater' cooledtubes `IV?!4and IVIIL. is accomplish'ed.itlorugh` capacitors ICIIliJ, i648, {C102}nI'C'I)3,\IC49-ari'd IC'I05; t i 'The cond'ensers ICI'IlIi7 ICM-and.4I'C |02 are equal sinlii'falue,` respectively, tocondensers ICII33,i049,- -'and i I CI 052 Y'Ihei Values'Vv of` the upper-"three ca- Y so:niet tric?cciipiiiigcap'acitiesfoni bein si'd'eslof s115fiiniitingswitch uncut, circuit to; n y

stage yand Voutv mpliiiedA output 4*of theidriverfstage vconsisting ofC81 v'and fICI'GBj The condensers are I "range-'lof lowerfrequencies,additionaliby- Y 4` the plate coil ILIB are equal.

voltage will be applied Vto the grids of the nal power amplifier tubesfor different operating conditions. f

From the foregoing, it will be observed that deriser divider;Hence',`as'"`long a'sdilie= radio fre- Y quency plate voltage of thedriverrstage' is held constant, the condenser divider serves to mainofYIV9v andIV fiiloverra very wide frequency range. By. virI-,ue'offth'eycondenser divider tuning, the driver'outputVY ys'tag'c'can beA adjustedover the entire freque'c'y'raige without affecting the ratio niegacyclescan be covered withthree com-binations `rof thecondesersj VinVthjefvoltagedivider byme'ans of the tapsf'on coilV III-TIE"andi'bych'angf.

ing the position and :coupling of -a short-circuited iRmcA. Asindicatcdycaeof "the iai-,ter is conriected-n series Vwith thel-'grdo'ftube LV?) fand 'Ivmjo'f the power amprer. y maestrias-'chores 151450'4and inscri and radio frequency 'by-passjconde'nser lciatrhaveibeen Kprovided inv tlfiegrid circuit of thepower' arnpli-V y after,areprovided. for the power amplifier. Itubes -IzVQ Yandflfill'..k:'Also', vasi-will 'be describedmore fully-' h'ereinafter,theitankcircuit of the power amplifier comprises" the'V inductanceIL5I', tuning condenser I CI I 2'; short-circuitin'gl strap.SB, con- Y.-byepassng condenser ICI'Z-and be; described moreifully hereinafter;comprises Athe inductor-11152,` tuningcondenser'ICI I4 and fixedcon'de'nse'ers` 'IC-I I 5' tot IC I 22a inclusive'.` Motori-driven;adjustment or tuning ofr various put circuit are provided; Thus;'greversiblez electrifc` motorj lAgdrives, neutralizing condensers .i Y

IGI-0B andICrlf'l. Directiongof-g'rotation is conf- 60 trolled byVswitchY I-S'I. Limiting-switches dia- IAM. 1n# other v'vo-rdVs'-,Vmotor-'IAiZIlj simultanen ne missiles 111A;

n this way, proper' I the input capacity of the powerv amplifier tubes.Imi-arid I.V,I;forrn thev lwrvoltagefllegs of a`con-V tainja'Acorrespondingly constant excitation volt- Y age to the power amplifieracross the power tubes of driver plateftopower amplifier grid radio fre-Y quency voltage. Actually some fixed adjustment of ,theV couplingcapacitors ofthevoltage dividerV Y arrangement'may, be required." Wehave found thatY the enti-'re'- range from -sixtotwenty-two the other'in series with theg'rid fof theothertube Also,-Y it' will be` heentirerange `of Y,

Y from and lleida; f which will 'be describedin greater detaill-ierein-n 'elements :in the power amplifier :stage and out:`

gramatically inditdf et' *,ILSI 2': and LS1! 3;, limit fr' 'Y the amountof-,rotationgo-ffthe-motor in either 'is 'ineffeci la voitmeter,inegccitage Jor de- IISISQISZIJ and ISAZI, and indicators IMIS, IMIII,'IMIS 'and- IMI'Il are provided for adjusting and indicating the'adjustmentI of `condensers ICI I2, coupling between inductors IL5I-'an'dIL52-and condenser ICI 4. Supply voltage for the` tuning indicatingsystem is derived' from the rectifier arrangement IASB. Motor drivingpower is furnished through leads'IB and 2A. The power supply to theseleads may be, for example, 220 volts 60. cycles A. C. current.

The limit switches, such as" ISIZ and ISI3, may'. be operated by cams,in turn operated or driven by reduction gearing coupled to the motorIA20, so that after a given numberof revolutions in one direction, limitswitch ISI2 will be opened and after a given number of revolutions inthe other direction limit switch ISI3 will be opened. Similarly, thepotentiometer and tap arrangement |R43 and 40B may be controlled byreduction gearing also coupled to the motor IA29, the tap being incontact with and moved )Over a circularly. shaped potentiometer, Similarcomments arev applicable to the other limit switches and potentiometerscontrolling the tuning indicators T|, The latter are provided withby-passing condensers |C`|5 to |C'|9 inclusive.

A preferred electrical and mechanical arrangement of the various partsof the power amplifier system and output circuit are shown in Fig- -ures2 to 8 inclusive. One vfeature of the arrangement consists in anassembly wherein the coupling of the output circuits comprising IL52with the preceding circuit comprising |L5I may be varied without varyingthe tuningY of the output circuit and wherein the tuning of the outputcircuit may be varied without changes in coupling.

As brieflystated before, Figure 2 is a side elevational, view fthe'power amplier assembly comprising tubes |V9 and IVI 9; Figure 3v isa front elevational View of Figure: 2; Figure 4 is a sectional view ofFigure 2; and Figures 5, 6, '7 and 8 illustrate arrangementsand'adjustments for the power amplifiel` tank circuit comprising IL5|for different frequency ranges.

Turning to Figure 3, radio frequency excitation from the driver stage isfed to the grids of the power amplier tubes IV9 and IVIO at the gridinput terminals 33, 83 and 33', 83. Two `leads, to each grid areprovi-ded which are connected together and to external circuits at 54and'54.

The neutralizing condensers ICIG'I and I CIIJB of. Figure 1 areillustrated in Figures 2 and 3 and `are seen. to comprise rounded orrectangular plates 56 directly attached to the tube anodes by means ofbrackets 56A and 56B. The variable plates of the neutralizing condensersare plates 59, 6|) each of which is of U-shape, so as to partiallysurround each of tubes V9 and VID. These U-shaped plates 59, 60, fixedtogether by insulating strip 59A, are simultaneously rotated on hinges64, 64A by the operation of the motor IA2IJ. This follows since rotationof motor IA20 is translated into movement of condenser plates 59 and 6Uby means of drum DI, cable 91 and vinsulating supporting anchors 63, 63Aappropriately attached to the plate 59, 60.

Individual adjustment of the neutralizing condensers may be made byadjustment of the wing nuts (not shown) at points 54, whereby thecondenser plates 56 may each be independently adjusted with respect tothe simultaneously moved condenser plates 59, 60, This can be done sincethe brackets 56A and 56B are slotted s'o-that the. condenser plates 56may be moved laxially along and fastened in aydesired position withrespect to the vacuum tubes V9 and :VIII and, of course, with respect tothe movable condenserplate combination 59,60. The tank circuit condenserICI|2v of Figure 1 'is'alsoillustrated in Figures 2 and 3. This con'-`motor casing and bracket cam and slotted apparatus. The cam and slotapparatus is shown more clearly in Figure 2 at36 and 31.

Cooling water is fed to the anodes of the vacuum tubes through theinsulating coils 24, 25 which provide for direct current insulation fromground. The cooling water is also fed and removed through the straightsections of insulating pipe 20 and 2|. AThe latter offer highimpedanceto and effectively insulate the tube plates from ground forradio frequency currents.

As shown in Figures 2, 4, and 8 the inductive portion |L5I of thetunable tank circuit of Figure 1 consists of metallic tubing 339, 34Dand 34|. This tubing 339, 349 and 34| is removably `xed vto the anodesby means of the wing nut operated flanges 5|.

Also, the inductor |L5I of Figure 1 may include for certain frequencyranges portionsof the vertically movable inductors 325, 325A of `Figures2 and 4. This movable inductor portion 325, 325A is supported bystand-01T insulators |46 upon an edge-rounded rectangular metallic`plate 32| which is fed with plate voltage through conductive strapv|83(Fig. 2). Metal plate 32| in turn is'insulatingly supported from agrounded metallic plate 3I5 by means of additional stand-off insulators3|6. y

Grounded plate 3I5 has attached thereto threaded spindles` 3|9cooperating with internally threaded sprockets 3| 3, in turn supportedby grounded metallic pedestals 3H). Motor I AZI drives suitable gearreducing `mechanism within the motor casing and the latter through bevelgear mechanism BGM and sprocket S drives chain 326. Chain 326 causessimultaneous operation of all ofthe sprockets 3| 3, resulting inmovement of the entire assembly upwardly or downwardly. This assemblyincludes'ground plate 3I5, anode or B voltage plate 32|, and theapparatus supported by rectangular plate 32| which apparatus includesinductor 325, condenser I C|23 and choke coil IL56. The direction ofrotationof motor IA2| and, hence, the direction of movement of theassembly depends upon the position to which switch ISB of Figure 1 isthrown. Movement of the assembly changes the inductance between thebottom turn 325, 325A and the upper turn 33,9, 340 which is fixed inposition and clamped as illustrated at 5| to the anodes of vacuum tubesV9 and VID. In this way, .the total tank inductance is changed,decreasing as the assembly is lowered and increasing as it is raised andthe turns 339,` 340 and 325, 325A brought closer together. This changein inductance gives one control on the tuning on the tankcircuitcomprising IL5I of Figure 1. Another lcont-rol 'onprad-justmentbf this ,tuning haslaly Vready been mentioned. namely,.adjustment of and reversiblemotor 1|A23.

.Abetterunde'rstan'ding of .the manner in which the plate tankvcircuit'fincluctance',may be :varied Vmay be shad by referringrtoFigures 5,6, 7 and v8,

which :diagrammatically .illustrate connections VAand adjustments.forvvarious frequency bands. i Y.

.Aszshown'in Figure, ,the upper tank conductors 339, 34D are fixed inposition ,andconnected at itheirright handterminals, as indicateddiagram-` .matically, to the anodes of tubes lVS vand 5|V|0. They areinsulatingly supported by :the insulating supports 51,5113, ,as alsoillustrated in Figure 4. Also, as shownin Figure 5,.the plate 32|,corresponding `to plate 32| of Figure '2,.supports the stand-oilinsulators |156, inductors 325, 325A, con- .denser 1C |`23,'and chokeVcoil .|L56. Choke lcoil m55-and condenser ICI23 are movable within theguide 323 along the plate 32| and in rthis lWay can have one of theirterminals connected to vthe adjustable short circuiting bar SB. Theinductance |LI of Figure 1, as illustrated in Figure .5, consequentlymaybe traced from the 'plateoftube IV9 through conductor 339,.the right"hand flexible connector '34B tothe right along .conductor 325A, acrossvmetal bar SB electrically connected to and slidable along conductors325 and 325A, then along inductor .325 to the left, 'throughrthe left.hand lflexible strap 355 and then valong conductor34n 'to the plate oftube IVM).

iThe'upperplateSSt of condenser|C|23 of Figures v2r and l5 is connectedby strap 387 to the shortcircuitingbar SB. The .choke ILES is ,con-`:nected to the short circuiting bar SB by strap 333 =of"-Figures 2 and5. The lower plate of con-y denser |C|23 rests upon vand .is therebydirectly vvconnected to'plate 32|. The capacityoflCl2'3 may be adjustedby moving the Wing nuty and pole arrangement supportingtheuppercondenser plate'386.

' As shown inlFigure 5, the lnductance of the Y tank circuit of 'thepower amplifier stage conlsists effectively of two turna-in which thebottom 'turn 325, '325A is moved relative tothe fixed top turn 339,r3150, This inductive system yhas beenl 'found :useful 'for 'the range:of frequencies running 'from 6.0 to approximately 98 megacycles.Obviously, for various frequencies within this range'the Vposition ofthe'short circuiting bar on theinductors 325, -325A'is changed and thesepalration of the turns 339, 3,40 and 1325, 325A'may vbe adjustedasbeforedescribed.- l

For Vthe frequency range runninggfrom 9.8 .to 10.5 megacycles, the`general arrangement of the "parts and adjustments are 'illustrated *inFigure `6. vFor this 'range the :snorting Vbar SB is moved -to the.extreme left hand end of the lower in- /ductors 325, 3125A.

For a frequency lrange of Vfrom -l0;-5 to 13.8 megacycles, the lowerinductance bars are not used at all, the straps 345 inthat ,eventbeingconnected, as illustrated 2in Figuref', to only the lupperV 'inductors339, 3153 Yand "to 'the condenser |Cl23. The `choke m in this -casehas:one fof "its terminals connected through strap .333 'to the 'snorting'bar.SB, as shown,` .For still'higl'er'frefquenci'es, namely, v*forexample, for arrange of Lfrequencies running "from 113.8 fto .222\mega'cycles,

,8 n .the iarraneementcis ,shown 58,. In that case, fthe ,lowerinductors 325 and ,'32 5A .are Ldisconnectedzffmrn :circuitand the-upperrinductol'. system previously. used is replaced-.Joy

Iinductors' 34| having a `'llfrger lconductor :dia-m.- veter than ltherpreviously vemployed pipes ,or tubes .si-3am, y v Y vlieferring toFigure V2,1it -Willbe Y'found :the

.condenser plate arrangement 3|5, 32| ,improves stability and tends tolessen :the setting21110.y `.0f

parasitic oscillations. Ther plate voltage lead |83 isfggrounded forradio1frequencycurrentsfby means Yof .the condenser iQ-|24, as,illustrated .more clearly in liiguire 22. c

, The inductance Vlof .the output'circut |L52 vof ,Figure 1 consistsof aportion of the :hairpin in-v ductor L52 orLLEZA ofFiguresfl .and'2.h.The coil of the larger conductor size L52Aiis employed-for the `higherfrequency range fsuclfry as, vfor example,

Cuit. 'Iheiiixed condenser tanks. |C||5 '.tof|;Cf|.22 K inclusive ofFigure 1 are similarly illustrated in Figures 2 and 4. y

The variabley plates of :condenser Figure lare illustrated in Figure 4at'3| and 310A, each consisting'of .a substantially rectan` .gularmetallic plate having rounded Vcorners'.and

rounded Ledges. AThesemovable condenser plates Vare provided with,metallic dishpan vsupports :i314 in turn supporting `stand-off:insulators SBS-.exi-

tending through-rounded .off perforations through vthe movable plates'.310 and 313A'. In .this v.v'vay electric stress on the,stand-oizinsulators' isre duced rWhile at :the same :time permittingthe ,movable plates 370' and 310A rto beibrought closerto-thegroundedplate.358. "Rectangulargrounded 'plate 358 .extends acrossvand is thereby capacitively coupled to both Vof themovabletplates.'311'0 and 310A; '.Thisais clearfrom an A,inspection of Figure 4. Y

Referring again to Figure 2,.by means` of :motor .|,A25anditsreducinggearing driving the sprocket SPI, v.chain V325A and theremainingtsprockets SP2, SP3, SP4, ,SP5 ,and SP5, fthe latter three.

being 'directly behind SPL SP2;` and-SP3, condenser. plates3|5 andiSTBAareadjustedina vertical direction. The sprockets are supported upon ,thepedestals V365which in `turnare fastened to the condenser Y'plate 353.J'The lsprockets are. in-

lternally threadedzand the 'threads thereof fengage .the v'threads on'the spindles .361, 368,:and 368A it-hereby .causing .movement 'of' vthe.movable .plates 33.0 and 31 A With-'respect tothe common condenser.plate :358 inla `direction perpendicular to the.planesoftlie.condenserplates. Fromwhat has been said'it should .beclearfth'at the spindle,sprocket -andmotor mechanism .|A25, SPI, i368, etc., is similar tothespindle chain and sprocket driving ymechanism Adescribed for .movingtheV plates '315, 4325| and the apparatus supported thereby.

In a Asimilar Way motor .IAM .operatesythe sprocket, chain .and .spindlemechanism 313B,

321B, 353B, 353B andliA .whereby .the-.entire assembly of i-riductor`unitV |1352 and 'condenser |C| [A is moved -in'ra vertical'zdirection;"Hence,

operation of motorl .m25controlstheituning Iof the .output .circuit.independently of the coupling `to the tankcircuit, and operation ofgmotorflAZll lmaybe usedtocontrol the coupling of themat- -put circuit.tothe ,platecircuitofg the power fampliasillustratedin'. Figure Y erwithout altering the tuning of ythev output circuit vcomprising I CII4.It is to 'be notedthat movement'oi the output assembly also includescondenser ICI I up to and including ICI22.

The output from the output circuit is taken through flexible conductingstraps 38| and 38IA to suitable terminals supported upon insulators 385.From the latter terminal a conductive strap CS3 brings the amplifiedhigh frequency waves to suitable insulatingly supported output terminals35| and 35IA as shown in both Figures 2 and 4. As explained inlconnection with Figure l, the various electric motorsare mechanicallycoupled by reduction gearing and other mechanical instrumentalities tochange tuning of condensers, coupling, etc. "Also,v additional gearingis provided whereby each motor mechanically drives the movable armof apotentiometer which may be arranged in the form-of acircle. For example,as shown in Figurel, motor IA2I drives rheostat arm 4IB of potentiometerIR44. The potentiometer arrangement is illustrated somewhatschematically to the left of motor IA2I in Figure 2 at point IRM.Similarly, for example, the potentiometer associated with motor IA24 isillustrated at IR45 in the upper part of Figure 2 and the potentiometerassociated with electric motor IA25 is illustrated at I R41, also inFigure 2.

Other parts of the apparatus illustrated in Figures 2, 3 and 4 should beself-evident to those skilled in the art, for example, the steelframework of the system and filament transformers T26 and T2l, blowermotor AIB (Fig. 3-top), filament by-passing condensers ICI |18, ICI $9,etc., and ICI 25 of Figure 1. Also, it is to be noted that the gridchokes IL50 and IL59A of Figure 1 are illustrated in Figure 3, as isalso condenser ICI3I). The stand-01T insulators with corona shields 9for the tube sockets I0 and II are illustrated at 8 in Figure 2.

Having thus described our invention, what we claim is:

l. A variable inductor arrangement comprising a pair of conductorsmounted in relatively fixed position, another pair of conductorsinsulatingly mounted upon a metal plate, connections connecting saidconductors serially` together, and apparatus for moving said plate andsaid insulatingly supported conductors with respect to said fixedconductors whereby the inductance of the serially connected arrangementmay be varied.

2. High frequency apparatus comprising a metallic plate, a ,pair ofsubstantially linear conductors insulatingly supported upon said plate,an adjustable short-circuiting bar connected across said conductors, acondenser having one terminal connected to said short-circuiting bar andanother terminal to said plate, a high frequency choke having oneterminal connected to said bar and its other terminal to said plate,said choke and condenser being movable along said plate as saidshort-circuiting bar is moved along said conductors, a circuit formaintaining said plate at positive potential with respect to ground, aby-passing condenser connected between said plate and ground formaintaining said plate at ground radio frequency potential, another pairof substantially linear conductors arranged substantially parallel tosaid insulatingly supported linear conductors, connections I forserially connecting together all of said conductors, and apparatus formoving said plate with respect to said fixed conductors in order toeffectively vary the inductance of 'said serially connected conductors.

' 3. In a high .frequency system,- a-pair of vacuum tubes each having anan'od'e, a pair -of linear conductors connected to said anodes,said'anodes and linear conductors being supported in rela'- tively fixedposition, a second-pair of linear ncon'- ductors arrangedparalleltofsaid `first pair, fiie'xible` connections between saidconductors'fsaid second pair of linear conductors being 'insulatinglyvsupported upon a 'substantially rectangular; metallic plate,l a'short-circuiting. bar movablel along and electrically connected tosaid-pair of insulatingly supported conductors, a'lcodenser. connectingsaid short-circuiting bar toi-said metallic plate, a radio frequencychoke coil connecting said metallicb'ar to said plate, a source ofdirect current voltage connected-to saidplate' whereby direct currentvoltage 4is `fed` fromusaid source to said plate and through saidchokecoil, short-circuiting y-bar, linear conductors,` andthe flexibleconnections therefor to` said anode'syandl a lay-passingcondenser'connected between said metallic plate and ground formaintaining said plate at substantially ground radio frequencypotential.

4. Apparatus as claimed in claim 3, characterized by the provision ofmechanical apparatus driven by a reversible electrical motor for movingsaid plate and the conductors insulatingly supported thereon closer toand further away from said conductors which are relatively fixed inposition, whereby the inductance of the circuit connected between saidanodes may be varied.

5. In combination, a U shaped inductor, means for feeding high frequencyenergy thereto, a second U shaped inductor arranged parallel to thefirst, an output circuit connected to said second U shaped inductor,said second U shaped inductor being arranged so that the plane of itsconductors is substantially parallel `to the plane of the conductors ofthe first mentioned inductor, and mechanical apparatus under` thecontrol of a reversible electrical motor for producing relative movementof said inductors in a direction perpendicular tothe planes of theconductors of said inductors.

6. High frequency apparatus comprising a looped conductor forming aninductance and a high frequency circuit coupled thereto, said circuitcomprising another looped conductor forming an inductance, and aplurality of condensers electrically connected thereto, apparatus foradjusting the inductive coupling of said loops without substantiallyaffecting the tuning of said circuit, and apparatus for adjusting thetuning of said circuit without substantially airecting the couplingbetween said looped conductors.

7. High frequency apparatus comprising a first looped conductor forminga first inductance, a second looped conductor forming a secondinductance and arranged substantially parallel to the first, a groundedmetallic plate of substantially rectangular shape upon which said secondlooped conductor is insulatingly mounted, a pair of condenser platesconnected to opposite sides of said second mentioned conductor loop andbeing adjustably supported between said loop and said metallic plate,means for moving said oppositely connected condenser plates physicallywith reference to said grounded condenser plate, and means for movingsaid ground plate, movable plates and second conductor loop as a unitwith respect to said iirst mentioned conductor loop.

8. Apparatus as claimed in claim '7, characterized by the fact that saidmovable condenser plates are moved by means of mechanical appamoon saidrectangular grounded metal plate, said movable plates Vbengrmounted'between said ine ciuctorfandv said grounded plate `and being con'-nectedfto opposite sides of said inductor. v

: 10. High frequency apparatus comprising an extensive metallic plate, ahigh frequency choke 2&12531@ coil. insulatingly supported uponsaidplate; a di*` recti` current circuit' connectedftc said plate 'formaintaining said plate at ahigh direct current voltage with respect toground, means' connecting one terminal of said choke to said pla-te'landits .other .terminal to high frequency apparatusga condenser having oneterminal connected to ground, and'means for connectingthe'vothertermin-al of said condenser to said'plate foriniain'a taining the lattertential. l. or 11. ApparatusI as claimed in claim 10 characat groundradiov frequencyfp terized by the fact that said metallic plate'is supported by stand-off insulators upon a second me- -tallic platearrangedsubstantially parallel to said rst mentioned plateywsaid Isecond mentioned platebeing electricallyconnected to ground: y

THOMAS JAMES Y BOERNEBQ JOHNAW` sANBoRN.- Y

